1. Technical Field
The present invention relates to image processing performed in the case of performing color display using four colors of sub-pixels.
2. Related Art
As an arrangement of the pixels in a display device using three primary colors, there can be cited a stripe arrangement and a delta arrangement (see, e.g., JP-A-07-006703 (Document 1)). In such a display device, each pixel is composed of three sub-pixels. Further, in a Bayer arrangement, each pixel is composed of four sub-pixels although the number of colors is three, two sub-pixels are assigned to green (G), one sub-pixel is assigned to each of red (R) and blue (B), and these sub-pixels are arranged two by two in the vertical and horizontal directions.
In the display device having the pixels configured using the Bayer arrangement, the color display is generally performed using the image data with quarter as many pixels as the pixels of the image data input therein. In this case, since the resolution of the image data used actually becomes lower than the resolution of the image data input therein, a filter process for limiting the frequency band of the image signal is performed to thereby suppress the moire caused by the alias. For example, in the case of the R and B image signals, in order for preventing the moire caused by the high-frequency component, it is necessary to limit the frequency band of both of the vertical and lateral directions to a half (i.e., ½) thereof. It should be noted that since the G image signal has twice as many sub-pixels as the R or B image signal, the limitation range of the band can be smaller than these.
Incidentally, there is a case in which the color display is performed using four primary colors (or more primary colors) for the purpose of improvement of color reproducibility or brightness. For example, JP-A-2006-267541 (Document 2) discloses the image display device having either one of the G sub-pixels in the Bayer arrangement replaced with white (W) or cyan (C) sub-pixel to thereby perform the color display with four colors of sub-pixels. Further, JP-A-2000-338950 (Document 3) discloses a technology for calculating the color image signals of the respective colors in the case of having a color display section of four or more primary colors. It should be noted that the “primary color” mentioned here denotes the color forming a base of the color mixture (an additive process), and is not limited to the light's three primary colors.
In the case of performing the color display with the four colors of sub-pixels, if the band of the image signal is limited for each of the colors independently from each other, the image signal of either sub-pixel is limited to a half in the frequency band in both of the vertical and lateral directions. However, if such a band limitation is performed, the information lost from the original image increases.